Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to automatic warewashers for cleaning dishes, glasses, pots, pans, kitchen utensils and the like; and in particular to apparatus for automatically dispensing detergent into the warewasher.
2. Description of the Related Art
Commercial kitchens have equipment to clean and sanitize dishes, glassware, and cooking utensils which are collectively referred to herein as xe2x80x9ckitchen ware.xe2x80x9d Such equipment, which is commonly known as a xe2x80x9cwarewasherxe2x80x9d or xe2x80x9cdishwasher,xe2x80x9d has a cabinet defining an internal chamber into which trays of kitchen ware are placed for washing. A washing and rinsing apparatus within the chamber includes a plurality of nozzles from which water sprays onto the kitchen ware being washed. The lower part of the cabinet forms a tank that collects the water which then is repeatedly circulated through the nozzles by a pump during the wash cycle. Then fresh water from an external supply line is fed through the nozzles during the rinse cycle. As the rinse water flows into the tank, some of the tank water overflows into a drain thus replacing some of the water from the wash cycle. The water is not completely drained from the tank between washing operations and thus contain detergent from a previous wash cycle.
A relatively large amount of detergent must be added when the tank is initially filled with water prior to washing the first batch of dishes and glasses. Thereafter, additional detergent has to be added in smaller quantities at the start of each wash cycle to replenish the detergent that drained away during the rinse cycle.
Systems have been devised to automatically add detergent into the cabinet. The basic automatic system always added the same predefined quantity of detergent at the start of each wash cycle. This quantity remained constant regardless of variation in water quality, soil condition of the dishes, and the amount of detergent remaining in the tank water. Thus these systems often added too much or too little detergent. Adding more than the necessary amount of detergent is wasteful and expensive, while adding less detergent than is needed results in the kitchen ware not being properly cleaned.
An improved automatic detergent control system used a probe that measured the conductivity of the water in the tank. Because the detergent is an alkali, the water conductivity varied with the detergent concentration. Therefore, by sensing the water conductivity, the control system was able to determine how much detergent needed to be added at the beginning of a wash cycle. Although this system resulted in more economical use of detergent, the conductivity probe became fouled over time by the build-up of lime from the water. Thereafter, the probe provided false indications of the water conductivity because the lime deposits reduced the conductivity of the probe. Thus an inaccurately low conductivity measurement was produced that caused more detergent to be added than was necessary. The solution to this problem was to clean the conductivity probe periodically by hand with a lime dissolving chemical, usually a weak acid solution. However, until that cleaning occurred the system continued to consume a greater amount of detergent than was needed.
An apparatus for dispensing detergent into a warewasher has a reservoir that contains the detergent. A flow control device is coupled to the reservoir and controls the flow of detergent into the warewasher. A sensor detects an amount of detergent present in water held in a tank of the warewasher. In the preferred embodiment of the apparatus, the sensor measures the electrical conductivity of the water, which varies with changes in the concentration of detergent.
A controller, connected to the sensor, operates the flow control device to dispense detergent into the warewasher. The controller has a first mode of operation in which a quantity of detergent being dispensed is determined in response to the amount of detergent detected by the sensor. The quantity being dispensed brings the amount of detergent in the tank water to a desired level to properly clean the kitchen ware. In a second mode of operation of the controller, a predefined quantity of detergent always is dispensed into the warewasher without reference to the amount of detergent present in the tank water at the commencement of a wash cycle. The controller selects between the first and second modes in response to a determination regarding reliability of operation of the sensor.
In the preferred embodiment, the operation of the sensor is determined to be reliable when the measurement of the electrical conductivity changes by at least a given amount upon detergent being dispensed into the warewasher. Otherwise the sensor operation is determined to be unreliable.